The aims of the proposed research are 1) to study the structure of the platelet plasma membrane and relate this to platelet function, 2) to study platelet aggregation and the adhesion of platelets to nonplatelet surfaces and reversal of these phenomena, and 3) to study the interaction of blood components at interfaces between blood and certain solid and semi-solid surfaces. The basic premise of this research proposal is that much more can be learned by combining biochemical and ultrastructural approaches than by pursuing either or both approaches separately. A wide range of ultrastructural and biochemical techniques will be used to realize the proposed aims; most of these techniques are already in use in our laboratory. The platelet plasma membrane will be studied by conventional and high resolution transmission electron microscopy, by scanning electron microscopy, and by radioautography. Particular attention will be paid to the outer portions of plasma membranes and to the space between aggregated platelets and between platelets and foreign surfaces to which they are adherent. Ultrastructure will be correlated with biochemical data whenever possible. Mechanisms responsible for platelet adhesion and aggregation will be studied. Special attention will be paid to possible forces responsible for these phenomena and to their diminution or reversal by specific agents. Reactions between blood components and solid surfaces will be investigated. The nature of the layer of adsorbed plasma proteins which forms on surfaces almost instantaneously upon their exposure to blood will be investigated. A study will be conducted of the effects of this adsorbed layer on platelets.